Syros had been inhabited since antiquity — the philosopher Pherecydes, who is said to have taught Pythagoras, was born here around 600 BC. Homer's Odyssey mentions an island called Syros, described by the swineherd Eumaeus as his homeland, though scholars debate whether this refers to the Cycladic island or somewhere else entirely. During the Byzantine period, Syros belonged to the Theme of the Aegean Sea. After the Fourth Crusade in 1204, Venice took it, and the island spent centuries under the Duchy of the Archipelago, acquiring in the process a Roman Catholic majority that proved surprisingly durable. When the Ottomans arrived in the sixteenth century, Barbarossa captured the island in 1522, but local negotiations secured religious freedom and tax reductions for the islanders. France and Rome extended protection to the Catholics. Syros became known, somewhat improbably, as 'the Pope's island.' It was a place that knew how to negotiate its way through larger forces.

Ermoupolis — the name means 'city of Hermes,' god of commerce — was essentially invented between 1822 and 1860. The refugees who poured in during the 1820s brought capital, skills, and commercial networks from their home cities. They laid out streets, built warehouses and churches, established banks and insurance brokerages. By 1831, under Greece's first governor Ioannis Kapodistrias, the population of Ermoupolis had reached 13,805. The city had a Commercial Court of Law, one of the first post offices in Greece, an art gallery, a museum, a library, and a social club. The German-born architect Ernst Ziller designed the town hall. The Italian Pietro Sampò built the Apollo Theatre — a miniature La Scala, right there on the Aegean. The shipyard called Neorion, established on Syros, was the first in Greece. For a brief, astonishing period, this island outpaced every other city in the country for commerce, industry, and sophistication.

The great buildings of Ermoupolis went up between 1822 and 1865, in a neoclassical style that married Greek classicism with Renaissance elements and the romanticism the European architects brought with them. Public buildings, churches, schools, mansions — all in the same idiom, all in pale stone, all part of the same argument that the new Greek state belonged to European civilization. Until 1860, Syros was the most important commercial harbour in Greece. Then steam replaced sail, and the logic of geography shifted. Piraeus, closer to Athens and the new railway, was better placed for the new technologies. Patras competed from the west. Syros lost its position, gradually and then all at once. The Apollo Theatre still stands. The neoclassical facades still line the streets. But the city that built them found itself, by the late nineteenth century, in the position of a man who had won a race that no one was running anymore.

Syros carries its religious history in the landscape. On the hill above Ermoupolis, Ano Syros is a Catholic town founded during the Venetian period, its medieval lanes leading up to the Cathedral of Saint George. Below, in Ermoupolis itself, the Orthodox majority worships at the Church of the Metamorphosis and at Kimisis tis Theotokou, which holds a painting by El Greco. Intermarriage between the two communities is common, and has been for generations. The Catholic diocese on Syros today numbers some nine thousand worshippers. The most celebrated figure in its history is Ioannis Andreas Kargas, a bishop whom the Ottoman authorities strangled in 1617 after he refused to convert to Islam. He had been helping Greek revolutionaries hiding on the island. Syros has always been a place where the currents of Mediterranean religion and politics intersected with unusual complexity.

Syros remains the administrative capital of the Cyclades, a function that outlasted its commercial dominance. Ermoupolis, the island's main city in a wider island population of around 21,000 at the 2021 census, still holds the regional prefecture. The Neorion shipyards still operate — still building and refitting vessels, just as they did in the 1860s. Tourism has grown, and the island's beaches and its neoclassical architecture draw visitors who come not just for the sea but for a city that feels different from the typical Cycladic experience. Syros is an island of cheese (San Michali), of loukoumi and halvadopita, of rebetiko — the Syros-born musician Markos Vamvakaris is a foundational figure in that blues-inflected Greek tradition. Stamata Revithi, the first woman to run the Olympic marathon (albeit unofficially), was born here in 1866. Demetrius Vikelas, the first president of the International Olympic Committee, was a native of Ermoupolis. Small islands sometimes produce outsized histories. Syros keeps proving it.